Re: kernels and b0xen
On Thu, Jan 23, 2003 at 01:48:29PM +0100, Geert Uytterhoeven wrote:
> On Thu, 23 Jan 2003, Gabriel Paubert wrote:
> > On Thu, Jan 23, 2003 at 12:12:56PM +0100, Geert Uytterhoeven wrote:
> > > BTW, I get 45 MB/s for the buffer-cache on my 66 MHz SDRAM.
> >
> > Looks still very low, very conservative bridge timings? This means a
> > cache line read (32 bytes) every 700ns or so. Even if you dirty every
> > cache line, doubling the traffic, this means 350ns per burst transfer.
>
> Note these are the results of `hdparm -T', not from a real memory benchmark.
> Real memory read performance is ca. 100 MB/s, which is reasonable for machines
> of that age, cfr. http://home.tvd.be/cr26864/Linux/PPC/MemSpeed.html
Ok, this means 90 or 135 MB/s on the bus, depending on whether
copy_to_user() uses dcbz or not. It should AFAIR, but I've not
looked at the code in a very long time. Depending on how the chips
is configured, dcbz may take quite some time too. In any case a far
cry from the theoretical half GB/s.
Waiting for the PPC970 to see how much of the theoretical 6.4 GB/s
you can actually get in RL...
Gabriel.
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